Method of coloring and hardening steel



March 3, 1936.

H. J. N. vom-MANN METHOD 0F COLORING AND HARDENING STEEL UNITED sTATEs PATENT OFFICE METHOD OF COLORING AND l' STEEL Henry J N. Voltmann,

Brooklyn, N. Y., assigner to W. S. Rockwell Company, New York, N. Y.,

a corporation of New Jersey Application September 29, 1934, Serial No. 746,232

3 Claims.

My invention relates to a method of coloring and hardening steel. The method is adapted to the treatment of steel and to imparting different colors to the metal. While it is particularly 5 intended for use in the production df uniform razor blades with a uniform blue color, it is equally well adapted to the coloring and hardening of other products not only in strip or sheet form, but also in the form of tools, automotive parts and numerous other articles of steel. As is well known a blue color has been imparted to steel and especially to tool steel by drawing and tempering operations. The blued 'steel thus produced has not the requisite degree of hardness for the production of razor blades. In order to provide a sumciently hard and o'therwise satisfactory cutting edge the blade must'be drawn back or tempered at a temperature (below 400 F.) relatively lower than that required for the production of blue oxide (between 500 to 600 F.)

The production of blued steel by annealing operations originally treated steel sheets in stacked relation, subjecting the Asheets to an oxidizing agent at a comparatively high temperature and then lowering the temperature. The diiliculty of -uniformly lheating or cooling steel while thus packed in a mass made it practically impossible to produce uniform razorblades of uniform color by such methods.

To obtain a product having the desired characteristics of hardness and uniformity of the cutting edge it has been found necessary to treat steel sheets or strips singly. The methods more recently employed, whether producing blued or plain blades, have involved the heating of the sheets or strips to a high temperature and rapidly chilling the heated steel. Where the blue color is not desired the heating is effected under customary furnace conditions. Where the blue color is to be producedon the hardened steel it has been proposed to carry out the heating to a high temperature (approximately 1400 F.) while the steel is enveloped in an oxidizing'gas, the introduction of the gas for coloring and the application of the high temperature for hardening being performed simultaneously. By this method the gas employed `for coloring the steel is introduced at a high temperature, at or above the critical or hardening point of the steel and considerably higher than the temperature required for the blueing operation.

In other words, the simultaneous cololring and heating for hardening have been performed at a temperature approximating that required for y hardening, and considerably higher than the temperature required and best suited for the blueing operation. At this temperature (approximately 1400 F.) the steel has a bright color.

The action of combustible gas at temperatures as high as 1400 F. orthereabouts is not clearly understood. Working with the gas at such temperatures is a delicate operation and is liable to give unexpected and unsatisfactory results. The composition of most gases is affected by such temperatures, so that the use of the diiferent gases suitable for imparting a blue color or other color to the steel is made dimcult and uncertain by the performance of the coloring operation in the high temperature hardening furnace and atthe high hardening temperature. Different performance, more convenient operation and better results can be obtained by use of the gas or gases at a lower temperature.

My invention cdntemplates the production of a blued or colored sheet or strip by effecting the blueing or coloring with air or a suitable gas at a relatively low temperature (less than 1000 F.) and well below the critical temperature of the metal and the ignitionvpoint of the gas and subsequently heating the blued or colored metal to a higher temperature in a non-oxidizing atmosphere that does not affect the color established by the lower temperature.

The method which constitutes my invention consists in performing the coloring operation prior to and independently of the operation of heating for hardening.

The method further comprises the performance of the coloring operation at a relatively low temperature and a subsequent heating for hardening at a higher temperature.

. The principal advantages of my method are better control of the finish; ease of varying the color of the metal by variation of the temperature or nature of the gas used for the coloring operation performed in a low temperature coloring zone out of the hardening zone and independently of the hardening operation; less danger of ex- 45 plosion; and elimination of odors or deposits from breakdown of the gas at the higher temperatures. By my method the coloring operation is performed under conditions best suited for eifecting the desired results and does not in any way affect the proper hardening of the steel.

In practice my method is well adapted, but not limited, to the continuous coloring, hardening and tempering of a razor blade strip.

The coloring and subsequent heating opera- 55 to utilize separate chambers for the coloring operations and the-subsequent high temperature heating for hardening, whether these chambers are separate furnaces or comprised in a single furnace. My invention does not reside in or depend upon the details of construction yof the furnace or furnaces employed. By way of explaining the method and its operation and as an example of equipment which may be used, reference may be made to the apparatus illustrated diagrammatically in the accompanying drawing.

In this illustrative and preferred example of vapparatus for carrying out my method the equipment comprises several units which may be individually distinct and separately mounted or may be combined and mounted upon a suitable stand adapted to be readily moved and handled as a single unit.

'I'he several units or sections of the illustrated apparatus are a low temperature oxidizing or coloring furnace or chamber I, a high temperature heating furnace or chamber 2 for hardening, a quench block 3 and a tempering unit 4. Suitable means (not shown) are also provided for pulling the razor blade strip 5 through the several units, chambers, sections or zones in succession, the strip being supported in any suitable manner for this purpose, for example, on a holding reel 6 and a take-olf reel 1. 'I'he designation of the units as chambers is to be understood in its broad sense as referring to compartments, sections or zones of a single furnace as well as to separate furnaces.

The coloring chamber I, hardening chamber 2 and tempering chamber l may be of any suitable construction, for example built with strong welded steel boxes lined throughout with insulating materials. The mullles 8, 9 and vided in these chambers or furnaces for the `passage of the steel strip therethrough may be either single or double muilles constructed of nickel chromium heat-resisting alloy or of anyV other suitable material.

The chambers or furnaces I, 2 andv 4 may be electrically heated or gas fired. The strip 5, being heated within the muilles 8, 9 and II) in either of these types of chambers does not come into contact with heating chamber gases. By this arrangement the operations of coloring and subsequent heating for hardening are carried out without interference and the same desired uniform quality and finish of the blades is obtained whether electric heating or gas firing is used in the chambers.

Provision is made for circulating air or introducing various other known oxidizing gases or liquids in the muille 8 of the coloring chamberv or section I. Considerable variation in the color of the strip can be obtained by circulating the air in the muiile 8 at different temperatures following generally the lines of procedure in the ordinary tempering processes. Different colors can also be produced by selection of suitable oxidizing or coloring gases, the identity, characteristics and degrees of oxidation capabilities of which are well known in the art. In lieu of air or gas, Veither or both at different temperatures if desired, low temperature liquid baths, for example, nitre or III respectively provarious suitable oils or chemicals, may be employed for immersion of the strip 5 in muille 8 of the coloring chamber I as a basis for and means of producing the color. Any suitable means may be provided for introducing, regulating and controlling the supply of air, gas or liquid to the mullle 8 into contact with the strip 5.

In any event, regardless of the particular oxidizing or coloring medium used, the treatment of the strip 5 therewith is carried out and the color 4fixed at a relatively low temperature, at or above the required coloring temperature, but less than 1000 F.

The muiiie 9 of the chamber, furnace section or furnace 2 is supplied, by any suitable Valved or otherwise controllable supply means, with a proper regulated quantity of a neutral or nonoxidizing gas, for example, nitrogen or carbon dioxide, to provide a non-oxidizing atmosphere in the muille 9 surrounding the strip 5 as it is drawn therethrough after having been colored in chamber I.

The invention is not limited to or dependent upon the use of any specific gas in muffle 9, there being Various gases, in addition to those mentioned, of well known characteristicswhich are suitable for this purpose; the choice of the particular gas is merely a matter of selection.

In the operation of my method the strip 5, after being blued or otherwise colored in the coloring unit, chamber, furnace or zone I, is transferred to the zone, chamber or furnace 2 to be heated to a higher temperature for hardening. The strip, while in chamber 2, is heated to a temperature of approximately 1400 F., or at or above the critical or hardening point of the steel.

Following this high temperature heating the strip 5 is successively drawn through the quenching block 3 and tempering unit 4. The block 3 may be formed of opposed water-cooled ground and polished .hardened steel plates, adapted to be opened by any suitable lever mechanism to insert the end of strip 5 at the beginning of the coloring and hardening operation and thereafter maintained in proper contact by tension springs or other devices suitable for this purpose. Block 3 preferably abuts or is disposed adjacent to chamber 2.

, .Automatic temperature controlling pyrometers may be provided for regulating the temperatures in the separate furnaces or in the respective zones of a single furnace where the latter form of furnace construction and arrangement is used.

It is to be understood, however, that the regulating means for controlling and varying temperatures and the supply of gas or air to the muiiies-of the furnaces form no part of my invention, such means generally being old and Well known in the art. The same is true of the chilling and tempering means and their details of construction. In other Words, my invention is not concerned with the particular construction tively low temperature within the temperature gas to` a temperatureat or above vthe critical `steel and range adapted to impart color to the subsequently continuing the heating of the colf ored steel to a substantially higher temperature at or above the critical temperature of the steel being treated, and finally chilling the steel.

2. The method of coloring and hardening steel which comprises subjecting the steel to an oxidizing gas and while so subjected heating the steel to a temperature substantially below thev critical point of the steel being treated and within the temperature range adapted to` impart color to the steel; maintaining the steel in heated condition; in. heated condition to neutral gas; the colored steel and heating while subjected to the neutral subjecting the 'colored steel While still point of the steel beiner treated.

3. The method of blueing and hardening steel which comprises introducing the steel into a coloring furnace and subjecting the steel in an oxidizing atmosphere therein to a relatively low temperature substantially below the critical point of the steel being treated and within the temperature range adapted to impart color to the steel; transferring the blued steel from the coloring furnace without intermediate cooling to a high temperature furnace, subjecting the blued steel therein to a temperature abovethe'critical point of the particular steel being treated in contact with neutral gas, and then chilling the steel.

. HENRY J. N. VOLTMANN. 

